This invention relates to a micro pipetting device that is adapted to dispense a small quantity of liquid samples such as reagents or the like with an exceedingly high degree of accuracy and reproducibility and, more particularly, pipetting devices of the type including a vertical cylinder provided on the lower end portion of a cylindrical housing, a piston working in the cylinder, an actuating rod connected to the piston and extending vertically through the housing, an operating knob mounted on the upper end of the actuating rod, a return spring biassing upward the actuating rod, and a tip mounted removably on the lower end of the cylinder for receiving therein and discharging therefrom liquid.
One example of the pipetting devices of the aforementioned type is disclosed in British patent specification No. 1,271,683 wherein the device is of the type including a vertical cylinder provided on the lower end portion of a coaxial cylindrical housing, a piston working in the cylinder, an actuating rod connected to the piston and extending vertically through the housing, an operating knob mounted on the upper end of the actuating rod, a return spring biassing upwards the actuating rod, and a hollow tip mounted removably on the lower end of the cylinder for receiving liquid therein and discharging liquid therefrom in operating the pipetting device. The tip has a conical shape and is snugly fitted on a frusto-conical lower end portion of the cylinder. The device can effectively restrain the contamination, however, there are shortcomings such that it is necessary to use a special apparatus in removing or mounting the tip, and that the device is not adapted to dispence a minute amount of liquid such as 10 .mu.l or less.